Taking gas samples from breathing circuits in anesthesia is a well known practice. It is desirable that the sample be taken at the patient. The sampling tube is one of several tubes associated with treatment of a patient. Being small and relatively fragile, the sampling tube is susceptible to damage by pinching or breakage. This is very detrimental when gas samples are relied upon for visual recognition and manual control, or for automatic control of administration of gases or other fluids.
Prior art U.S. Pat. Nos. 3,856,051 to Bain, 4,188,946 to Watson and Rayburn, and 4,320,754 to Watson and Rayburn disclose breathing devices in which a corrugated plastic breathing tube has a smaller tube extending lengthwise inside and terminating at the patient end for delivery of anesthetic gas to a patient. But to our knowledge, all gas sampling tubes used in the prior art are external to the breathing tubes.